Blender Git Loki

Cleanup: move off-screen drawing to view3d_draw.c

Since offscreen drawing now uses draw engine, this doesn't need to be
considered legacy.

Note that there are some calls into view3d_draw_legacy.c from view3d_draw.c
this is generally not accepted, so its only dont where there are checks
for new/old engine.
Functions exposed to do this use a VP_deprecated prefix.